Evaluation of specific metabolic rates of major organs and tissues: comparison between men and women

Abstract

Objectives: The specific resting metabolic rates (K(i) , in kcal/kg per day) of major organs and tissues in the Reference Man were suggested in 1992 by Elia: 200 for liver, 240 for brain, 440 for heart and kidneys, 13 for skeletal muscle, 4.5 for adipose tissue and 12 for the residual mass. However, it is unknown whether gender influences the K(i) values. The aim of the present study was to compare the K(i) values observed in nonelderly nonobese men to the corresponding values in women.

Methods: Elia's K(i) values were evaluated based on a mechanistic model: REE = Σ(K(i) × T(i) ), where REE is whole-body resting energy expenditure measured by indirect calorimetry and T(i) is the mass of major organs and tissues measured by magnetic resonance imaging. Marginal 95% confidence intervals (CIs) for the model-estimated K(i) values were calculated by stepwise univariate regression analysis. Subjects were nonelderly (age 20-49 years) nonobese (BMI 18.5-29.9 kg/m(2) ) men (n = 49) and women (n = 57).

Results: The measured REE (REEm) and the mass of major organs and skeletal muscle were all greater in the men than in women. The predicted REE by Elia's K(i) values were correlated with REEm in men (r = 0.87) and women (r = 0.86, both P < 0.001). Elia's K(i) values were within the range of 95% CIs for both men and women groups, revealing that gender adjustment is not necessary.

Conclusions: Elia's proposed adult K(i) values are valid in both nonelderly nonobese men and women. Further studies are needed to explore the potential influences of age and obesity on K(i) values in humans.

Figure 1a

Measured resting energy expenditure (REEm, in kcal/day) versus predicted REE (REEp, in kcal/day) for the men (Figure 1a) and women (Figure 1b). REEp were calculated from the Ki values suggested by Elia (1992), according to equation 3. The lines of identity are shown. REEm = 1.044 × REEp − 87.1, r = 0.874, P <0.001, n = 49 men.

Figure 1b

Measured resting energy expenditure (REEm, in kcal/day) versus predicted REE (REEp, in kcal/day) for the men (Figure 1a) and women (Figure 1b). REEp were calculated from the Ki values suggested by Elia (1992), according to equation 3. The lines of identity are shown. REEm = 0.855 × REEp + 201.7, r = 0.855, P <0.001, n = 57 women.

Figure 2a

The difference between measured and predicted resting energy expenditure (REEm – REEp, in kcal/day) versus the mean of REEm and REEp for the men (Figure 2a) and women (Figure 2b). REEp was calculated from the Ki values suggested by Elia (1992), according to equation 3. The zero difference lines are shown. (REEm – REEp) = 0.044 × REE mean − 87.1; r = 0.075, P >0.50; n = 49 men. The lines representing 2SDs for the REE differences (−149, 146 kcal/day) are shown.

Figure 2b

The difference between measured and predicted resting energy expenditure (REEm – REEp, in kcal/day) versus the mean of REEm and REEp for the men (Figure 2a) and women (Figure 2b). REEp was calculated from the Ki values suggested by Elia (1992), according to equation 3. The zero difference lines are shown. (REEm – REEp) = 0.0007 × REE mean − 2.7; r = 0.001, P >0.50; n = 57 women. The lines representing 2SDs for the REE differences (−192, 174 kcal/day) are shown.

Figure 3

The 95% confidence intervals (CIs) for the Ki values of seven organs and tissues, fitted by stepwise univariate analysis are shown on a logarithmic scale. The upper line is for the men, and the lower line is for the women. The Xs represent the Ki values suggested by Elia (1992). Abbreviations: AT, adipose tissue; Res, residual mass; SM, skeletal muscle.